This invention relates to an optical coupler for coupling coherent light from one single mode optical fiber to one or more adjacent optical fibers. More particularly, the invention is concerned with providing support for the optical fibers as they extend in close twisted or braided adjacency such as across a chamber of a housing where light is coupled from one fiber to another. To aid this light coupling, optical cladding of each of the optical fibers is etched thin to allow close adjacency of the optical cores.
There is disclosed in U.S. Pat. No. 4,264,126 by S. K. Sheem, entitled Optical Fiber-To-Fiber Envanescent Field Coupler, an arrangement for providing light coupling between optical fibers sealed in a bottle type housing. In that arrangement two cladded single mode optical fibers are twisted around each other over an extended distance with their optical claddings having been substantially etched away in the twisted region for allowing closeness of the optical cores. These fibers pass through an open chamber of a housing and out through sealed openings on opposite sides of the housing. A liquid such as oil, adapted to solidify upon curing, is introduced into the chamber where it defines an index matching material around the fibers. Means are provided for twisting the optical fibers to adjust their tension and maintain their adjacency for controlling light coupling therebetween. That coupler, termed a bottle coupler, because of its general appearance, is an optical power divider which serves as a beam splitter for use in optical arrangements where coherent light from a single source such as a laser is divided and caused to take separate optical fiber routes.
The single mode optical fibers used in bottle couplers are extremely small and fragile. Fiber breakage has been encountered due to environmental shock vibration, or differences in thermal expansion between the fibers and surrounding index materials. To circumvent this problem, several efforts have been undertaken to encapsulate the fibers in special epoxies and glues. In all cases, these efforts failed because expansion and contraction of the encapsulant was different from glass, thus causing breakage of the small optical fibers. The present invention is directed at providing sufficient mechanical support and protection for the small fragile optical fibers to protect them in their environment without interfering with light coupling therebetween.